Silent tuning system for radioreceivers



Dec. 31, 1935. N K 2,026,102

SILENT TUNING SYSTEM FOR RADIORECEIVERS Filed Jam, 27, 1935 3Sheets-Sheet l FIG. 6

FIGJ.

INVEYNTOR fl/ezan o'er 52ml u/fe ORNEY Dec 31, 1935. A ENAUKE 2,026,102

SILENT TUNING SYSTEMFOR RADIORECEIVERS Filed Jan. 27, 1955 5 heat Sheet2 4 n :5 d o 4 .'.I"" :8 ON: I; WY? 3 "2 g F, n l g h Ee- LL FIG.3

INVENTOR Alexander Jig/make ATTORNEY 31-, 1935. A, SENAUKE SILENT TUNINGSYSTEM FOR RADIORECEIVERS Filed Jan. 27, 1935 Sheets-Sheet 3 lNVENTORlZ/exander Jenna/ e W 6m ATTORNEY broadcast receivers,

Patented Dec. '31, 1935- SILENT TUNING SYSTEM v RECEIVE New York, N.

Jersey City, N. J. a cor Alexander Senauke, Hazeltine Corporation,poration of Delaware This application relates to' electrical jtuningapparatus and it is particularly advantageous in although itsapplication is not limited thereto. I

In certain-aspects my invention is an improvement on the apparatus shownand describedin my Patent No. 1,839,419 entitled Radio receiver and onmy applications Serial Nos.- 527,673 and 589,812, Patent #1,961'-,574granted June 5, 1934,

and as to certain parts thereof isa continuation in part'of saidapplications. v

In accordance with my invention, I provide a system by means of whichthe radio receiver or other apparatus in which the system is embodied,-is rendered unresponsive, at least in part, to incoming electricalimpulses and disturbances, dur- ;ing times when the receiver isnot tunedto a .justment of the tuning desired signal, and is rendered completelyresponsive to incoming signals merely by the adcuntrol to a frequency atwhich the receiver is at or near resonance with an incoming signal ofpredetermined strength.

Inaccordance with vention I obtain this result either without requiringthe use of any tubes or the like, other than those ordinarily providedfor amplification and detection purposes in the receiving apparatus, orby the use of a gaseous'discharge tube.

Inaccordance with still another-aspect of my invention, I combine asystem of the ciass,described with systems, such as those described andclaimed in my patent and applications above ref ferred to, in which avisual indicator, such as a lamp, is energized at the-settings of thetuning indicator "which correspond to exact resonance with incomingsignals.

Among the various objects of my invention, it is an object to provide aradio receiving system in result is obtained which noises, interferenceand the like, which might otherwise be heard, aresuppressed during thetransition period of tuning from one stationto another.

It is a further object ,of my invention to provide a system of the classdescribedin which the I without the necessity of providing additionalvacuum tubes in or associated with .the receivingapparatus.

It is a further object of my invention to provide such a system which iscapable of adjustment so as to exclude not only noises and various typesof undesired. electrical disturbances, but also 'to exclude undesiredsignals, the strength of which may be insuflicient to be pleasing to thelistener. v

It is a further object of my invention to pro-' Application January 27,1933, Serial No. 653,795 f Claims. (01. 250-) another aspect of my inlcationof Fig. 4;

such manner that the in other types of receivers,

pied to cell 2. andmay FOR RADIO- RS Y., assignor to vide a systemo'ithe class described utilizinga visual indicator, such as a lamp, forgiving a light signal to show when the receiving apparatus is tuned to'exact resonance with the incoming de sired signal.

It isstill a further object of my invention to providesuch a system inwhich a gaseous discharge lamp. may be-utilized to .accelerate ormagnify the action of the apparatus in changing from responsive tounresponsive condition and vice versa.

Still other objects and advantages of my inv ventidn will be apparentfrom the specification.

The features of novelty which I believe to be characteristic of myinvention are set forth with particularity in the appendedclaims. Myinvention itself, however, both principles and as to its willbest beunderstood by reference to the specification and accompanying drawings,in which Fig. 1 represents one embodiment of the circuit accordingto myinvention;

Fig. 2 is a characteristic curve of response of an electronic dischargetube which may be utilized in accordance with my invention; 1

Figs. 3, 4 and 5 are modified forms of circuit in accordance withimyinvention;

'Fig. 5 is a partial circuit diagram of a modifi- Fig. 6 is apartial'circuit diagram of a modification of Fig. 1; and l V Fig. '7 isa partial circuit diagram of a modification of Fig; 3.

Referring now more particularly to Figs. 1 and 2, I have shown in Fig.-1 acircuit arranged- .followed by a detector and audio amplifier, but

it will be understood that'my inventiomis not limited to such receivers,but may also be applied such as so-called superheterodyne receiverswhich may be consid-' ered as acting in essentially the same manner, andsubject to the same type as regards the principles of my invention. I

Ldesignates a signal collecting device of any suitable type. such as anantenna, connected to the coil2..grounded as at 3. Coil 4 may becoutuned circuit of the receiver, which is completed by blockingcondenser 6 and condenser l.

as to its fundamental particular embodiments,

voltages developed in the normal action of the circuit will produce asilence of control insofar The tuned circuit so formed may be grounded,

comprise an anode 8, a cathode l0 and, if desired, a heater I! forheating the cathode It to electron emitting temperature.

' I do not desire to limit myself to the use of any' particular type ofthermionic vacuum tube, since a number of well known types of'tubes willoperate as desired, and it will be understood that types of vacuum tubesother than that shown may be utilized if desired, such for example asthe so-called screen grid tube. For purposes of simplicity I haveomitted portions of the hearing circuits of the various tubes, sincethese arrangements are well-known in the art and form per se no part ofmy invention.

The cathode it of the tube '3 may be .connected to ground throughcondenser l2 for a purpose which will be later explained, and thecondenser may be shunted by resistance [2a. The output of tube l ispassed through coil i3 which is in turn coupled to coil It, andassociated with the coil N are the blocking condenser l6 andthe turningcondenser l5, forming another tuned circuit. 7

A second vacuum tube II is similarly associated with the second tunedcircuit and the output of tube I1 is passed through coil I9, which iscoupled to coil 20. Vacuum tube 25 may in this case be the same type oftube employed in the preceding stages, or a different type, but it may,and in some cases preferably will be, ar-

ranged for operation as a Fleming valve, the control electrode 26 andthe anode 2% being connected together for this purpose, and the signalbeing impressed between the cathode 27 and the electrodes 2d and 26, theinput circuit consisting of coil 25 and resistance 2|. Resistance 2i maybe shunted by condenser 22. v

The low potential side of coils i and It may be connected together andto conductor I0, and interposed in this conductor 10 I may provideresistance 53. The low potential end of coil 20 may be connected toconductor Ill on the opposite side of resistance 53, through aninterposed inductance 23, and conductor T0 leads to condenser 29, thencethrough resistance 30 to conductor 60 which, in turn, is connected tothe blade of switch 5|, which I term the noise gate switch, the functionof which will be described hereafter.

The lower terminal of resistance 30 may be connected to ground throughcondenser 3|, as indicated, and tap 32 may be provided as a manualvolume control for varying the magnitude of impulses impressed on thefirst audio frequency amplifying tube may be fed through transformer 34to'the input of a second audio frequency amplifying stage indicated asso-called output is combined by transformer 31 and supplied to asuitable indicating device such as the voice coil of a loud speaker 39operating in a magnetic field produced, for example, by coil 38.

. Since the construction and operation of the audio frequency amplifiersubsequent to tube 33 and loud speaker herein diagrammatically indicatedis well-known to and understood by those skilled in the art, andconstitutes per se no part of this invention, the same is not shown ordescribed in detail.

The apparatus thus far de:cribed may be energized in'any suitable manneras by batteries or 33, the output of whichother source of directcurrent, but customarily a so-called power pack will be employed foroperating it from alternating current, and this may take the formindicated, in which Q!) is the primary of the power transformer having anum- 5 bar of secondaries M, 42, t3 and M3 for providing alternatingcurrents of different voltages.

45 indicates a thermionic rectifier of'the full wave type, the filamentof which is energized from secondary winding 42, and 45 represents achoke interposed on the positive side of the rectifiedcurrent line forthe purpose of smoothing out fluctuations. M and 48 are filtercondensers connected between the positive and negative sides of thecircuit for the further smoothing out of i5 fluctuations, and since thisconstruction is well understood in the art no further description isbelieved necessary.

Transformer secondaries t3 and 4% may be utilized to supply rawalternating current to the 20 filaments of the various tubes, and themid-point of winding 43 may be grounded through resistance-BI shunted bycondenser 58.

The lower terminal of coils l3 and I9 may be connected together toconductor 50 and resistor -33 5i grounded through condenser l8 and to asuitable point on resistances 55, 56 and 5? which are connected betweenthe positive side of condenser 39 and ground, thus providing the desiredvoltage for the'anodes of tubes 1 and ii. :11)

The field coil 38 of the loud speaker may be connected through conductor66 to the lower terminals of condensers 48 and ll and its other terminalgrounded.

Connected to the common point of resistances 3-) 56 and 5'7 I mayprovide a conductor its leading to 'noise gate switch contact 6311.

Thenoise gate switch ti in one position may engage contact 63a and inthe other position may engage a contact 66a connected to conductor- Cit,4c

grounded through resistance 65.

For the purpose of providing for magnified noise control and for avisual tuning indication, if desired, I may provide the gaseousdischarge tube generically designated as 10, which is pref- 4.1

erably a tube of the type obtainable on the market under the nameTun-A-Lite, consisting, in one form, of an envelope containing gas at arelatively low'pressure, such as neon at a pressure of a fewmillimeters, and having within =7 the envelope a short cathode H, ashort anode .12; and a long cathode l3. The anode 12 is connected to thelower potential point of resistance 5| as indicated, the short cathodethrough limiting resistance 14 to conductor 63, and the long 13 cathodeto conductor E l.

With the noise gate switch 6| thrown to engage contact 63a, the noisesuppressing action of the circuit is eliminated, and it functions simplyas an automatic volumecontrol receiver, which ac-ffi) tlon will now adescribed.

The cathodes of the tubes 1 and II are 'connected to ground throughresistance In while the grids of the said tubes are not. However,

the grid potential with respect to ground is fixed .03

by the conductiveconnection of the grids of these tubes throughconductor 10, resistance 53, radio frequency choke 23, and resistance 25to ground, and the effective grid bias on these tubes is determined bythe I. R. drop due to the space current 7 therein in resistance [2a plusthe I. R. drop through resistance 53 I which may be neglected, since noappreciable current flow exists in resistance 53) and by the I. R. dropin resistance 2! due to the space current flowing in tube 25. 7:

It will be understood that when space current flows in tube 25, the endof resistance 2| which is connected to the cathode, becomes morepositive with re pect to the other end, and the greater the spacecurrent in tube 25, the greater will be this I. R. drop. This dropcomprises three components: (1), a radio frequency component which maybe by-passed by condenser 22; (2), an audio frequency component which itis desired to amplify for operating the loud speaker; and, (3), a meandirect current potential which is utilized to obtain the automaticvolume control action.

The radio frequency component is prevented from reaching the grids oftubes 1 and I1 by the action of the by-pass condenser 22 and also by theradio frequency choke 23. The audio frequency component is isolated fromthe grids of tubes 1 and H by resistance 53 and condensers 5 and I6, andit will be apparent the stronger the signal, and therefore the greaterthe space current in tube 25, the more negative the mean directpotential of the grids of tubes 1 and I1 will become with respect totheir cathodes.

If now the various resistances be so chosen that when no signal is beingreceived the tubes 1 and H are delivering maximum space current, and asignal is received, the increase in signal produces an increase in thenegative bias of the tubes 1 and I1, which decreases theiramplification. I

For the strongest signals there will-be the least amplification and forthe weakest signals the greatest amplification in the tubes I and I1.Consequently, the system tends to maintain a constant volume leveldependent upon the initial setting of the various elements, regardlessof the strength of incoming signals.

As will be understood, the audio frequency component of the spacecurrent of tube 25 passes through condenser 29 and resistance 30 toground through condenser 3|, producing an audio frequency voltage dropin resistance 30 which, or the desired portion of which, is impressedupon the audio frequency amplifier tube 33, amplified by that tube,further amplified by tubes 35 and 36, and delivered to the voice coil ofloud speaker 39. 3

Since the operation of the system from the output of tube 33 forms perse no part of my invention and is well known in the art, it is notdescribed in detail.

It will also be noted that with switch 5| in engagement with contact 63athe grid of tube 33 is self-biased" negatively with respect to thecathode thereof by an amount equal to the drop through resistance 94 dueto the space current of tube 33, and is substantially independent of'signal strength and consequently no selective noise-suppressing actiontube 33. I

The noise suppression action of this circuit will now be described.

Referring now to Fig. 2, I have shown the long cathode space currentcharacteristic of the gaseis developed by the ous discharge tube betweenthe long cathode and anode plotted against voltage for a condition ofconstant ionization; that is to say, when anode 12 and short cathode 1|are connected through limiting resistor 14 acrossa source of voltagesufficient to maintain ionization within the tube, and it will be notedthat if the voltage between the long cathode 13 and anode 12 increasesupto a certain value, the space current increases very slowly andmaintains a relatively small value, which for practical purposes may beneglected.

At a certain voltage a very small increase in voltage produces arelatively sharp increase in space current, as indicated by the lowerknee of 5 the curve. Increased in voltage beyond this point producerelatively large and constant increases in space current until the tubebegins to reach saturation. This characteristic is utilized to obtainmagnified noise control in the circuit of Fig. 1. 10

It will be noted that when the switch 6| is thrown to engage contact64a, the bias between grid and cathode of tube 33 includes the I. R.drop through resistance 65 and that through resistance 51 as well asthat through resistance 94. 15

It will also be noted that resistance 51 is traversed by a currentflowing from the positive to the negative side of the power pack, themagnitude of which may be controlled by adjustment of any one of theresistances 55, 56 and 51, and 20 hence the I. R. drop throughresistance 51 may be selected as desired. Also, the drop in potentialbetween the positive side of the power pack, and upper, or negativeterminal of resistance 5|, may be controlled by varying the position ofthe 25 tap onresistor 55.

' Assuming that the various resistances have been so chosen or adjustedthat a satisfactory volume level is maintained for the weakest signaldesired, it is possible to adjust the tap on resistor 55 until 30 thereceiver just goes dead. This will occur when the tube 33 is overbiasedto an extent sufl'icient to render it unresponsive. Therefore, signals,and also noise, of lower strength will produce no response in the loudspeaker.

If the value of the said resistance and the position of the tap onresistor 55 have been so chosen that when no signal is being received(and maximum space current is flowing in resistance 5|), and the voltagebetween the long cathode 13 40 and anode. 12 is just below the lowerknee of the curve of Fig. 2, there will be nodischarge on the longcathode 13 and no glow will appear thereon.

If now a stronger signal be tuned in, the negative bias on the grids oftubes 1 and I1 will be increased, as already explained, the current inresistor 5| will decrease, and the potential of the top point ofresistor 5| will rise. This in turn increases the voltage effectivebetween anode 12 and long cathode 13 above the lower knee of the curvein Fig. 2 and, the cathode 13 will suddenly begin to take substantialspace current, which flows from the top of resistance 5| to anode 12, tocathode 13, through resistance to ground, (thereby making the upperterminal of 55 resistance 55 more positive than the lower terminal),thence through resistances 51, 56, a portion of 55, and resistance 5|,back to the starting point.

This action, producing a sudden difference of potential in resistance55, the magnitude of which is'sufliclent to reduce the previous overbiason tube 33 to the normal operating bias, this tube will then amplify theaudio frequency variations impressed upon it. (30

Also it will be noted that when the input circuit of tubes 1 and I1 istuned to resonance with the incoming signal, the space current will bedecreased to a minimum for that particular signal. Likewise the voltagedrop through re- 7 sistance 5| will be at minimum for that particularsignal, and the voltage effective between long cathode 13 and anode 12will be at maximum, and consequently the glow on cathode 13 will climbto a maximum point.

As resonance is passed, the space current of tubes 1 and I1 begins toincrease, the voltage drop through resistance 5I begins to increase, thevoltage effective across cathode 13 begins to decrease and the dischargerecedes.

When the voltage reaches the lower knee of the curve in Fig. 2, thedischarge suddenly decreases, the drop through resistance decreaseslikewise, and the negative bias on tube 33 suddenly increases sharply,carrying the tube to its cut-off point, whereby it will be observed thatas the receiver is tuned in the intervals on the dial between signals,the receiver will be unresponsive and as a signal is tuned in, thereceiver will suddenly become responsive, the glow will appear oncathode 13 and will indicate by its maximum height when resonance hasbeen reached. After resonance is passed, the reverse action occurs.

The tap on resistor 55 may be utilized for the purpose of providing amanual volume level control for selecting minimum audibility of signalsdesired to be heard. In the arrangement shown, the tap will be moved upwhen noise level is low and down when the noise level is high, thusrequiring a stronger signal to open the receiver when noise is high.

For purposes of example and not of limitation, in the circuit shown,satisfactory results have been obtained when resistance 5| is of theorder of 6,000 to 10,000 ohms, resistance 14 is of the order of 100,000to 500,000 ohms, and resistance 65 of 10,000 to 25,000 ohms.

Referring now more particularly to Fig. 3, I have shown a slightlydifferent modification. In this arrangement the receiver is arrangedsubstantially as before, but it will be noted that some slight changesare made in the power supply apparatus. For instance, the field coil 38of the loud speaker is utilized as a second choke on the positive sideof the power supply, being connected by means of conductors I04 and I05in series between the upper terminals of condensers Q8 and 49. In thisinstance, resistances I00 and II are connected in series between thepositive and negative points of the power supply, by means of which asubstantially constant current flows through resistances I00 and IOI,producing a substantially constant voltage drop therethrough. The anodeof tube 33 is connected to a suitable point of positive potential andthe cathode thereof is connected to a point on resistance IOI.

When the noise gate switch 6| is thrown into engagement with contact63a, thereby eliminating the noise suppressing action of the circuit, itwill be noted that the grid return of tube 33 is taken to a point onresistance IOI more negative than the potential of the cathode, whichpoint may be selected to provide the normal operating negative bias fortube 33.

In this instance the short cathode 1| of the gaseous discharge tube isconnected to the switch contact 64a. The anode 12 is connected toresistance 5i, as before, the other terminal of which is provided with astop which may be adjustable on resistance I00.

The short cathode 1i may be connected through resistance I06 toconductor I02, representing the most negative point of the system, andthe long cathode 13 is connected to conductor I01, which is alsoconnected to switch contact 63a.

The noise suppressing action with the switch in the position shown is.as follows:

The position of the tap from resistance 5|, as before, serves the noisegate level, is adjusted so that the voltage between the anode 12 and theshort cathode 1| is just below the striking voltage. Therefore, nocurrent flows through the gaseous discharge tube and the effective gridbias on tube 33 is the entire drop of potential between the negative endof resistance ml and the point to which the cathode is connected, andthis is chosen sufiiciently great to overbias the tube 33 to cause platecurrent cut-off.

When a signal of sufficient strength is tuned in the plate current flowin tubes 1 and I1 decreases as before, causing the potential between theshort cathode 1| and the anode 12 to rise. When the striking voltage isreached, a discharge takes place between the short cathode and theanode, causing an instantaneous jump in voltage between the shortcathodeand ground equal to the difference between the striking voltageand the working voltage of the tube, which is usually from 10 to 15volts. This voltage appears across resistance I06 and thereby decreasesthe bias on the audio tube 33 by this amount, which is sufficient toreduce the over-bias on this tube to an amount sufficient to permit thetube to function.

The long cathode 13 of the gaseous discharge tube is connected to apoint on resistor IOI about ten to fifteen volts positive with respectto ground, so that further decrease in the space current flowing throughresistor 5| and the tendency thereby to increase the voltage between theanode 12 and the long cathode 13 causes the long cathode to take spacecurrent and the glow discharge appears on the long cathode and begins toclimb, and reaches its maximum for resonance. This serves as a tuningindicator and simultaneously tends to prevent the grid bias on tube 33decreasing unduly below the initial jump. Tuning of the receiver pastthe resonance point causes the current through resistor 5| to rise,thereby extinguishing the gaseous discharge tube and causing the tube 33to become again overbiased to plate current cut-off, silencing thereceiver.

Referring now more particularly to Fig. 4, I have shown still a furthermodification of apparatus according to my invention in which, in thisinstance, no gaseous discharge tube is utilized for the purpose of noisesupppression, that action being obtained by the use of only the tubesotherwise provided for normal operation of the receiver. In thisarrangement the receiver circuit shown is substantially the same asbefore, but in this instance it will be noted that the field winding 38of the loud speaker is connected by means of conductors H3 and H4between the lower terminals of filter condensers 48 and 39.

As before, the plate return from tubes I and I1 are connected togetherthrough resistance 5i to the positive point of the power supply system,and it will be noted that in this instance, the plate of tube 33,instead of being connected to a point of relatively unchanging positivepotential on the power pack, as in the previous arrangements, isconnected to the negative end of resistance 5|, to which the plates oftubes 1 and I1 are connected, and the plate of tube 33 therefore swingsin potential. When no signal is being received, and the space current oftubes 1 and I1 is a maximum, the plate voltage on tube 33 is a minimum.Conversely, when incoming signals are being received, the space currentof tubes 1 and I1 decreases, the drop through resistance 5I decreases,and the plate voltage rises. This change of plate voltage facilitatesthe blocking and unblocking of tube 33 under the control of a v ying ridbias, since the increase 01' plate voltage when signals are beingreceived facilitates the unblocking of the tube, and the decrease whenno signals are being received facilitates the blocking. The cathodes ofthe tubes I and II are connected together and through lead 54 andresistance 8 to ground. The cathode of tube 33 is likewise connected toground, but the grid return in this instance is connected as before tothe blade of noise gate switch 8 I. Resistances Ill and 2 are connectedfrom resistance Illl to conductor H3 and it will be noted that a tap 58may be provided for varying the value of resistance 2.

It will be noted that the anode current of the radio frequency amplifiertubes 1 and I1 flows through resistors 8, III and that portion of 2included by the tap. The drop through resistor H8 serves to self-bias"the tubes I and I! to their normal operating valu The common point ofresistances H8 and I ll may be grounded through conductor 52.

It will be noted that with the noise gate switch thrown to engagecontact 63a, the resistance III is included in the grid circuit of tube33, and this resistance is chosen of the desired value to maintain thenormal operating bias on-tube 33.

When, however, e noise gate switch 6| is thrown in the position shown,it will be seen that the bias on the grid of tube 33 includes the dropboth through resistor Ill and that portion of resistor H2 included bythe position of tap 53, and by moving the tap, the bias on tube 33 maybe increased to a point suflicient to cause substantial plate currentcut-off, 'at predetermined volume, or noise leve It will be noted thatin this instance, although the bias on the audio tube 33 varies with thesignal strength, it is possible to limit the variations of this bias towithin tolerable values by proper choice of the values of the variousresistors. The stabilizing action of the self-bias of the space currentof tube 33 will prevent too small a grid bias. I

If it is desired to magnify the noise supressing actiomor to provide avisual indicator for showing when the receiver is tuned exactly atresonance with an incoming signal, the apparatus shown in Fig. may beadded to that shown in Fig. 4 at the point indicated.

With the short anode 12 connected to the top of resistance 5| throughconductor 88, the short cathode ll may be connected through resistance14 to conductor 4 and the long cathode I3 may be connected to thecontact 64a by conductor 8L.

Resistance 82 is connected between conductor 8| and conductor 3.

With these additions and changes in structure, the operation of thesystem will now be described. If the noise gate switch 6| be turned toengage contact 63a, the noise gate suppressing action will be eliminatedand the tube '10 will function simply as a resonance indicator in thefollowing manner. A

The short cathode TI and short anode 12 are connected respectivelybetween the negative side of the power pack system and the negative sideif resistance 5|. Thus the eifective voltage is :h full voltage of thepower supply system, which s essentially constant, less the voltage dropin resistance 5|, which is a minimum at resonance. The value ofresistances 14 and 82 will be so :hosen with respect to thecharacteristics of the ;ube that the gaseous interior of the tube is inno space current is being an ionized condition, and there may be aconstant discharge between the anode I2 and the short cathode H. Undernormal conditions, with no signal being received, the voltage betweenthe long cathode 13 and the anode" will be a 5 minimum and no dischargeoccurs on the long cathode 73. However, when a signal is tuned in andthe plate current decreases, the voltage effective between the longcathode l3 and anode 12 rises, causing a climbing glow to appear upon 1the long cathode 13, and this climbing glow" reaches its maximum heightwhen the signal is tuned to exact resonance. In general, the strongerthe signal, the greater will be the potential across these electrodesand the greater 15 will be the height of the climbing glow on the longcathode 13.

When the noise gate switch is rotated to the other position, that is, toengage contact 64a, the bias eifective on tube 33 when no signal isbeing 2 received includes the voltage drop through resistances Ill and2, as already described with reference to Fig. 4, but it will be notedthat the grid circuit also includes resistance 82. When drawn by thegaseous discharge tube due to the action of resistance 5| alreadydescribed, no current flows through resistance 82 and the effective gridbias on tube 33 will be that developed by the drop through resistancesHi and H2 due to the space current of tubes 1, l1 and 33. When, however,the voltage eifective between the long cathode 13 and the anode 12increases to the point where the gaseous discharge tube begins to drawspace current, this space current flows through the resistance 82 andproduces a voltage drop of suflicient magnitude to overcome the overbiason tube 33 and to place the tube in operating condition.

As the receiver is tuned more closely to reso- 40 nance, the voltageeffective across the long cathode 13 and the anode 12 reaches a maximumand the glow appearing on the long cathode 13 reaches its maximumheight. As resonance is passed, this voltage begins to decrease, theglow likewise begins to decrease and when this voltage becomesinsufiicient to maintain the gaseous discharge in tube 18, space currentceases to flow, the potential drop through resistance 82 drops tosubstantially zero and the effective negative bias on tube 33'isincreased to the point of plate current cut-off.

In Fig. 6 I have shown an arrangement utilizing a gaseous discharge tubesimilar to the gaseous discharge tube used in Fig. 1, except that itcomprises four electrodes instead of three, the fourth electrode beingdesignated as lla and the four electrodes being secured within a singlepress in a straight line, the electrode Ha being disposed on theopposite side of the electrode 13 from electrode 12. The connections areessentially the same in Fig. 6 as in Fig. 1*except for the changesshown, in which resistance 55a instead of being connected to electrode13 is connected to electrode Ha and grounded at its lower 85 end. Itsupper end is connected to the contact 64a of the noise gate switch andthe electrode 13 is connected directly to ground. Electrode l2 isconnected as before to the junction of resistor 5| and conductor 58.

The arrangement of Fig. 6 has certain advantages over that of Fig. 1, inthat a considerably sharper cut-off betweena. responsive condition andunresponsive condition may be obtained.

That is to say, a smaller change of signal strength will sufllce tochange the receiver from responsive arrangement it will be noted thatresistor a corresponds to resistor 65 and serves to change the bias onaudio tube 33 from plate current cutoff to operating condition. Theoperation involves the same fundamental principles as before, it beingunderstood that when no signal is received the voltage existing betweenanode I2 and long cathode I3 is insufiicient to produce a dischargebetween the said electrodes and under these conditions, although anionizing discharge may take place between electrodes II and I2, nodischarge takes place between electrodes I2 and I3 or between I2 andIla. Consequently no current flows through resistor 65a and the audiotube 33 is overbiased to plate current cut-off.

When a signal is tuned in and the plate current of tubes I and I1 goesdown to a value sufficient to cause a discharge to pass betweenelectrodes I2 and I3, the discharge first passes to electrode I3 andinstantaneously also to electrode Ila, thereby producing a voltage dropthrough resistance 65a, which serves to reduce the grid bias on tube 33to an operative condition.

As the tuning approaches resonance the glow discharge on electrode I3climbs as before to a maximum at resonance and after resonance is passedrecedes and finally when the space current of tubes I and I1 increasessufliciently the voltage effective between electrodes I2 and I3 is nolonger suflicient to maintain the discharge, which thereupon stops, andlikewise the discharge from electrode Ila. ceases, thereby overbiasingtube 33 to plate current cut-off.

In the arrangement shown in Fig. '7, I have shown the adaptation of afour electrode tube to the circuit of Fig. 3. In this case the electrodeII is connected through resistor I25 to the common point of choke 46 andcondenser 48. Electrode.I2 is connected to the lower terminal ofresistor 5|, the upper terminal of which is connected as before. Thelong cathode I3 is connected directly to ground and electrode I20 isconnected to the switch contact 64a and also through resistance I26 .toground. Switch contact 63a is connected as before.

The electrode I20 may be of greater length than electrodes II and I2 andof lesser length than of the electrode I3 andits upper portion I22 maybe bent to project toward electrode I3. The portion of electrode I 20which would'otherwise be exposed within the tube may be enclosed with aninsulating shield such as a glass tube I2I which may extend from thepress nearly to the outer end of electrode I20.

By controlling the position of the end of electrode I20, that is, bymaking the electrode of greater or lesser length, it is possible tocontrolthe noise suppressing action very exactly, since it has beenfound that no current will pass to or from the electrode I20 until thedischarge on electrode I3 has climbed to a point approximate] in linewith the end of electrode I20.

The operation of the system is somewhat similar to the operation of thesystem shown in Fig. 3-, but differs therefrom in that the currentpassed by electrode I20 and which produces a voltage drop throughresistor I26, is used to overcome the overbias on tube 33.

It will therefore be understood that as a signal is tuned in and as theplate current of tubes I and II goes down, a discharge takes placebetween the anode I2 and the long cathode I3.

Unlike the arrangements already described this discharge does notimmediately cause the tube 33 to be rendered responsive, since thedischarge does not immediately jump to electrode I20. However, as thereceiver approaches resonance and the glow begins to climb up electrodeI3, it ultimately arrives opposite the end I22 of electrode I20 and atthat time electrode I20 begins to draw current producing a voltage dropin resistance I26 which serves to reduce the overbias of tube 33 to anoperating bias. As the receiver reaches resonance the glow on electrodeI3 climbs still further and as the receiver passes resonance it beginsto recede. When it passes the point opposite the end I22 of electrodeI20 the discharge from electrode I20 ceases, the voltage drop developedthrough resistance I26 disappears, and the tube 33 is overbiased toplate current cut-off.

By the utilization of the principles embodied in this arrangement, it ispossible to so adjust the receiver that a considerably smaller change insignal strength will open and close the receiver than with the otherarrangements already described.

While I have shown and described certain preferred embodiments of myinvention, it should be understood that these are by way of example andnot by way of limitation and that modifications and changes may be madewithout departing from the spirit and scope of my'invention, as will beunderstood by those skilled in the art.

I claim:

1. In a radio receiver, in combination, a signal selector, a circuitcomprising a thermionic relay, means for impressing a grid bias on saidrelay such as to render said relay unresponsive to impressed impulses,and means comprising a gaseous discharge device for impressing on saidrelay a compensating bias of magnitude suflicient to render said relayresponsive whenever the amplitube of incoming selected signals exceeds apredetermined level.

2. In a radio receiver, in combination, a signal selector, a circuitassociated therewith for receiving signals selected thereby andcomprising a thermionic relay having an anode, a cathode, and a controlelectrode, means for biasing said control electrode with respect to saidcathode to render said relay unresponsive to impressed signals, agaseous discharge device, means for producing a discharge in said devicewhenever the amplitude of selected signals exceeds a predeterminedamount, means associated with said discharge device for causing saiddischarge to produce a potential difference, and means for utilizingsaid predetermined conditions, a gaseous discharge device, means forproducing in said device a climbing discharge, the height of whichrepresents the magnitude of a desired function, and means for renderingsaid relay responsive whenever the length of said discharge exceeds apredetermined limit.

4. Control apparatus, comprising, in combination, a work circuit havinga thermionic relay, means for impressing a potential on said relay torender it unresponsive, a gaseous discharge device having a pair ofelectrodes arranged to produce on one of said electrodes adischarge thelength of which varies as a desired function, an additional electrode insaid discharge device arranged to take current only for predeterminedpositions of said discharge, and means associated with said additionalelectrode for impressing on said relay a potential to render itresponsive when 'said additional electrode is taking current.

5. In a radio receiver, in combination, a gaseous discharge devicehaving a relatively long elec-.

trode, means for producing a discharge on said electrode having amaximum length when said receiver is tuned to resonance with incomingsignals, and means controlled by said discharge device for preventingresponse of said receiver to selected signals except when the amplitudeof said signals exceeds a predetermined limit.

6. In electronic apparatus, in combination, 'a thermionic relay, meansfor impressing a potential on said relay to render it unresponsive,power supply apparatus for furnishing operating potentials to saidrelay, a gaseous dischargedevice having a pair of electrodes, one ofwhich is relatively long, means for impressing between said electrodes apotential which varies as a predetermined function and of sufiicientmagnitude to produce a discharge on said long electrode, the

- length of which varies with said potential, an impedance in circuitwith said discharge device for producing a potential derived fromcurrent passed by said discharge device, and connections for impressingsaid potential on said relay to oppose the potential rendering saidrelay unresponsive.

7.- In a radio apparatus, in combination, an amplifier, means fordecreasing the gain of said amplifier in accordance with the amplitudeof received signals, whereby said amplifier tends to maintain a constantoutput volume level, a second amplifier, arranged to amplify the outputof said first amplifier, means for biasing said second amplifier toplate current cut-01f, a gaseous discharge device, means for impressingacross said device a variable potential which is a maxi: mum when thecircuit of said first amplifier is in resonance with received signals,an impedance in circuit with the space path of said device, andconnections between said impedance and said second amplifier foropposing said first biasing means.

8. In a radio receiver, in combination, a signal responsive devicecomprised of a vacuum tube amplifier having an anode, a cathode, and acontrol electrode, means for supplying signals to said device, includingmeans for selecting the frequency of supplied signals, means forsupplying plate and grid voltages to said amplifier to render the sameunresponsive when no signals are being received, and means for producinga change in both said voltages to render said amplifier responsive whensignals of predetermined strength are being received. I

' 9. In a radio receiver, in combination, a signal responsive devicecomprised of a vacuum tube amplifier having an anode, a cathode, and acontrol electrode, means for supplying signals to said device, includingmeans for selecting the frequency of supplied signals, means-forsupplying plate and grid voltages to said amplifier to render sameunresponsive when no signals are being received, and means for producingan increase in plate voltage when signals of a predee termined strengthare being received.

10. Radio receiving apparatus, .comprising, in combination, a radiofrequency amplifier system having at least one vacuum tube amplifierhaving a cathode, an anode, and a control electrode;

. a detector and an audio frequency amplifier having a cathode, ananode, and a control electrode; an impedance associated with saiddetector to provide a voltage drop which increases with the strength ofincoming signals; a connection between said impedance and the controlelectrode of said radio frequency amplifier for causing the same tobecome increasingly negative with increase in signal strength; animpedance in the 5 space current path of said radio frequency amplifiertube, and a connection between the control electrode of said audioamplifier and said last named impedance for causing said controlelectrode of said audio amplifier to become less negative with respectto its cathode with increase in signal strength.

11. Radio receiving apparatus, comprising, in combination, a radiofrequency amplifier system having a cathode, an anode, and a controlelectrode, a Fleming valve detector and an audio frequency amplifierhaving a cathode, an anode, and a control electrode, an impedanceconnected between the electrodes of said detector and traversed by acurrent which increases with the strength of incoming signals, aconnection between said impedance and the control electrode of saidradio frequency amplifier for causing the same to become increasinglynegative with increased signal strength, an impedance in the .25

space current path of said radio frequency amplifier tube and aconnection between the control electrode of said audio amplifier andsaid last named impedance, causing the control electrode of said audioamplifier to become less negative with respect to its cathode withincrease in signal strength.

12. Radio. receiving apparatus comprising, in combination, a radiofrequency amplifier system having a cathode, an anode, and a controlelectrode, a Fleming valve detector and an audio frequency amplifierhaving a cathode, an anode and a control electrode, an impedanceconnected between the electrodes of said detector and traversed by acurrent which increases with the 4 strength of incoming signals, aconnection between said impedance and the control electrode of saidradio frequency amplifier causing the same to become increasinglynegative with increased signal strength, a pair of impedances connectedsignals of predetermined strength.

13. In a radio receiver, in combination, a radio frequency amplifiersystem having a cathode, an anode and a control electrode, a detectorand an audio frequency amplifier, means for causing the space current ofsaid radio frequency amplifier to decrease with increasing signalstrength, a gaseous discharge device having a relatively long electrodefor producing a discharge the length of which on said electrodeincreases with increasing signal strength, a second electrode associatedwith said long electrode and arranged to take current only when thelength of discharge of said long electrode reaches a predetermined valueand means controlled by said second electrode for modifying theoperation of said receiver.

14. In a radio receiver, in combination, a thermionic relay, means forimpressing a potential on said relay to render it unresponsive, agaseous discharge device having a pair of electrodes arranged 76 toproduce on one of said electrodes an expanding discharge the size ofwhich varies as a desired function, an additional electrode in saiddischarge device arranged to take current only for predeterminedpositions of said discharge, and means associated with said additionalelectrode for impressing on said relay a potential to render itresponsive when said additional electrode is taking current.

15. In a radio receiver, in combination, a signal selector, a circuitcomprising a thermionic relay, means for impressing a grid bias on saidrelay such as to render said relay unresponsive to impressed impulses,means comprising a gaseous discharge device for impressing upon saidrelay a compensating bias of magnitude sufiicient to render said relayresponsive whenever the amplitude of incoming selected signals exceeds apredetermined level, said gaseous discharge device comprising a pair ofkeep-alive electrodes, a

primary discharge electrode and a secondary discharge electrode arrangedto draw current only when said primary discharge electrode draws cur- 10rent.

ALEXANDER. SENAUKE.

